310 DIM A(2), D(2)
10 '         Sunrise-Sunset
20 GOSUB 300
30 INPUT "Lat, Long (deg)"; B5, L5
40 INPUT "Time zone (hrs)"; H
50 L5 = L5 / 360: Z0 = H / 24
60 GOSUB 1170: T = (J - 2451545) + F
70 TT = T / 36525 + 1: ' TT = centuries
80 '               from 1900.0
90 GOSUB 410: T = T + Z0
100 '
110 '       Get Sun's Position
120 GOSUB 910: A(1) = A5: D(1) = D5
130 T = T + 1
140 GOSUB 910: A(2) = A5: D(2) = D5
150 IF A(2) < A(1) THEN A(2) = A(2) + P2
160 Z1 = DR * 90.833: ' Zenith dist.
170 S = SIN(B5 * DR): C = COS(B5 * DR)
180 Z = COS(Z1): M8 = 0: W8 = 0: PRINT
190 A0 = A(1): D0 = D(1)
200 DA = A(2) - A(1): DD = D(2) - D(1)
210 FOR C0 = 0 TO 23
220 P = (C0 + 1) / 24
230 A2 = A(1) + P * DA: D2 = D(1) + P * DD
240 GOSUB 490
250 A0 = A2: D0 = D2: V0 = V2
260 NEXT
270 GOSUB 820: '  Special msg?
280 END
290 '
300 '        Constants

320 P1 = 3.14159265#: P2 = 2 * P1
330 DR = P1 / 180: K1 = 15 * DR * 1.0027379#
340 S$ = "Sunset at  "
350 R$ = "Sunrise at "
360 M1$ = "No sunrise this date"
370 M2$ = "No sunset this date"
380 M3$ = "Sun down all day"
390 M4$ = "Sun up all day"
400 RETURN
410 '     LST at 0h zone time
420 T0 = T / 36525
430 S = 24110.5 + 8640184.812999999# * T0
440 S = S + 86636.6 * Z0 + 86400 * L5
450 S = S / 86400: S = S - INT(S)
460 T0 = S * 360 * DR
470 RETURN
480 '
490 '  Test an hour for an event
500 L0 = T0 + C0 * K1: L2 = L0 + K1
510 H0 = L0 - A0: H2 = L2 - A2
520 H1 = (H2 + H0) / 2: '  Hour angle,
530 D1 = (D2 + D0) / 2: '  declination,
540 '                at half hour
550 IF C0 > 0 THEN 570
560 V0 = S * SIN(D0) + C * COS(D0) * COS(H0) - Z
570 V2 = S * SIN(D2) + C * COS(D2) * COS(H2) - Z
580 IF SGN(V0) = SGN(V2) THEN 800
590 V1 = S * SIN(D1) + C * COS(D1) * COS(H1) - Z
600 A = 2 * V2 - 4 * V1 + 2 * V0: B = 4 * V1 - 3 * V0 - V2
610 D = B * B - 4 * A * V0: IF D < 0 THEN 800
620 D = SQR(D)
630 IF V0 < 0 AND V2 > 0 THEN PRINT R$;
640 IF V0 < 0 AND V2 > 0 THEN M8 = 1
650 IF V0 > 0 AND V2 < 0 THEN PRINT S$;
660 IF V0 > 0 AND V2 < 0 THEN W8 = 1
670 E = (-B + D) / (2 * A)
680 IF E > 1 OR E < 0 THEN E = (-B - D) / (2 * A)
690 T3 = C0 + E + 1 / 120: ' Round off
700 H3 = INT(T3): M3 = INT((T3 - H3) * 60)
710 PRINT USING "##:##"; H3; M3;
720 H7 = H0 + E * (H2 - H0)
730 N7 = -COS(D1) * SIN(H7)
740 D7 = C * SIN(D1) - S * COS(D1) * COS(H7)
750 AZ = ATN(N7 / D7) / DR
760 IF D7 < 0 THEN AZ = AZ + 180
770 IF AZ < 0 THEN AZ = AZ + 360
780 IF AZ > 360 THEN AZ = AZ - 360
790 PRINT USING ",  azimuth ###.#"; AZ
800 RETURN
810 '
820 '   Special-message routine
830 IF M8 = 0 AND W8 = 0 THEN 870
840 IF M8 = 0 THEN PRINT M1$
850 IF W8 = 0 THEN PRINT M2$
860 GOTO 890
870 IF V2 < 0 THEN PRINT M3$
880 IF V2 > 0 THEN PRINT M4$
890 RETURN
900 '
910 '   Fundamental arguments
920 '     (Van Flandern &
930 '     Pulkkinen, 1979)
940 L = .779072 + .00273790931# * T
950 G = .993126 + .0027377785# * T
960 L = L - INT(L): G = G - INT(G)
970 L = L * P2: G = G * P2
980 V = .39785 * SIN(L)
990 V = V - .01 * SIN(L - G)
1000 V = V + .00333 * SIN(L + G)
1010 V = V - .00021 * TT * SIN(L)
1020 U = 1 - .03349 * COS(G)
1030 U = U - .00014 * COS(2 * L)
1040 U = U + .00008 * COS(L)
1050 W = -.0001 - .04129 * SIN(2 * L)
1060 W = W + .03211 * SIN(G)
1070 W = W + .00104 * SIN(2 * L - G)
1080 W = W - .00035 * SIN(2 * L + G)
1090 W = W - .00008 * TT * SIN(G)
1100 '
1110 '    Compute Sun's RA and Dec
1120 S = W / SQR(U - V * V)
1130 A5 = L + ATN(S / SQR(1 - S * S))
1140 S = V / SQR(U): D5 = ATN(S / SQR(1 - S * S))
1150 R5 = 1.00021 * SQR(U)
1160 RETURN
1165 '
1170 '     Calendar --> JD
1180 INPUT "Year, Month, Day"; Y, M, D
1190 G = 1: IF Y < 1583 THEN G = 0
1200 D1 = INT(D): F = D - D1 - .5
1210 J = -INT(7 * (INT((M + 9) / 12) + Y) / 4)
1220 IF G = 0 THEN 1260
1230 S = SGN(M - 9): A = ABS(M - 9)
1240 J3 = INT(Y + S * INT(A / 7))
1250 J3 = -INT((INT(J3 / 100) + 1) * 3 / 4)
1260 J = J + INT(275 * M / 9) + D1 + G * J3
1270 J = J + 1721027 + 2 * G + 367 * Y
1280 IF F >= 0 THEN 1300
1290 F = F + 1: J = J - 1
1300 RETURN
1310 '
1320 '   This program by Roger W. Sinnott calculates the times of sunrise
1330 '   and sunset on any date, accurate to the minute within several
1340 '   centuries of the present.  It correctly describes what happens in the
1350 '   arctic and antarctic regions, where the Sun may not rise or set on
1360 '   a given date.  Enter north latitudes positive, west longitudes
1370 '   negative.  For the time zone, enter the number of hours west of
1380 '   Greenwich (e.g., 5 for EST, 4 for EDT).  The calculation is
1390 '   discussed in Sky & Telescope for August 1994, page 84.
